The concept of clonal selection postulates unispecificity of lymphocytes. For B cells this law of clonal selection has been well established. All antibody molecules produced by one B lymphocyte have identical variable region domains. Thus a B cell presents on its surface, receptor antibody molecules of identical specificity. For T cells this law is implied but has not been adequately documented. Several obstacles have blocked progress in the study of T cell products. The biggest single obstacle has been the lack of cloned T cells exhibiting an immunological meaningful function or product. In fact, it is not certain that T cells bear clonally distributed receptors not that they secrete clonally distributed products. Recent experiments suggest that T cells exhibit "dual recognition" and further suggest the possibility of two receptors for antigen, each a "cloned product" on T cells. Recent studies in my laboratory have shown that in the murine system it is possible to derive clones of alloreactive T cells. The objectives of the experimental protocol outlined in this grant application are to isolate and characterize cell srface proteins and secreted products of cloned T cells. Once it has been established that T cells obey the tenants of the clonal selection theory for responsiveness to alloantigens and the clonally distributed products characterized, it should be possible to extend these studies and examine T cell receptors and products for a variety of stimulatory agents. Not only would studies on cloned T cells be of interest insofar as basic research concepts of clonally expressed products of T lymphocytes, but might be of more immediate use to advance the field of tissue typing and transplantation surgery, as well as in the potential production of specific immunotherapeutic tools to use in a variety of subspecialties in medicine.